This invention identifies and provides certain modifications to orthotic devices and enhances the elemental antipronatary orthotic described in U.S. Pat. No. 4,747,410. With reference to that antipronation orthotic, this invention includes a lateral column to supplement its antipronation effects. The addition of a lateral column, among other elements, facilitates correction of such conditions as severe pronation, rearfoot pronation and in-toe/out-toe gait problems.
The physiology of the various conditions is now described so as to facilitate a proper understanding of this invention. The conditions are presented in the following order: severe pronation, rearfoot pronation and, finally, in-toe/out-toe.
Commencing with severe pronation, reference is made to FIGS. 1-3 representing the midtarsal joint in the neutral, pronated and supinated conditions, respectively. The condition of severe pronation involves initial rearfoot eversion which causes pronation by depressing the First Metatarsal and Cuneiform below the Cuboid. Thus, the Peroneus Longus muscle is prevented from functioning properly. The improper rearfoot position adversely affects the Midtarsal Joint (the Midtarsal Joint is composed of the Calcaneal-Cuboid articulation and the Talo-Navicular articulation).
When the Subtalar Joint is neutral or supinated, the Talo-Navicular Joint is superior to the Calcaneal-Cuboid Joint (see FIGS. 1 and 3). If the Subtalar Joint is pronated, the two midtarsal joints are almost side by side (see FIG. 2). In the first case, oblique Midtarsal Joint Axis 11 is almost parallel to ground reactive force vector 13; weight bearing is thereby met with resistance from a solid, bone structure. When pronated, the two joints are adjacent, there is no bone structure to resist weight bearing and ground reactive forces 13 are sufficient to dorsiflex the forefoot on the rearfoot, thus causing skeletal imbalance and hypermobility. This is described in Sports Medicine, Otto Appenzeller, M.D., Ph.D., Ruth Atkinson, M.D., Urban & Schwartzenberg, Baltimore, Md. 1983, on page 406. When the Subtalar joint is neutral or supinated (FIGS. 1 and 3) the long axes 12 and 16 corresponding to the Calcaneal-Cuboid and Talo-Navicular directions of motion are oblique to each other. In this case the two joints are locked together because their directions of motion intersect, forming a solid bony structure. Contrarily, when the Subtalar Joint is pronated (FIG. 2) the directions of motion are parallel. Without intersection of the directions of motion, there is no locking of the two joints and hypermobility results.
Proceeding from the Medtarsal Joint to the forefoot, pronation causes the forefoot to turn into the ground (evert). In cases of severe pronation, continued forefoot eversion results in bunions and hammer toe conditions. Forefoot eversion results in further rearfoot eversion, thus perpetuating the pronation cycle until the rearfoot is maximally pronated.
Previous treatment of severe pronation included the use of prescription orthotics with rearfoot posting and a very high degree of forefoot varus. Such orthotics are difficult to construct accurately and fit awkwardly in a shoe.
Moving now to the physiology and kineisology of rearfoot pronation, an excellent summary is provided in Sports Medicien, Otto Appenzeller, M.D. Ph.D., Ruth Atkinson, M.D., Urban and Schwartzenburg, Baltimore, Md. 1983, page 408. The following was derived from that resource.
Given a normal foot (FIG. 4) the rearfoot is maximally pronated when the subtalar joint is everted 10.degree. . The eversion of the rearfoot directly affects the stability of the First Ray (First Metatarsal and Cuneiform) and , consequently, the entire mobile adapted - rigid lever sequence of the gait cycle. When the Subtalar Joint pronates (FIG. 5), the medial arch of the foot approaches the supporting surface; that is the first metatarsal and cuneiform descend. The Peroneus Longus muscle 19, attaching to the first metatarsal at the cuneiform articulation, will accordingly descend into the transverse plane. Muscle contraction under these circumstances results in transverse vector 23 directed away from the body midline (abduction). In this case, the downward component 22 of the muscle force is reduced to the point where it is insufficient to lock the Metatarsal-Cuneiform joint into the rigid lever configuration thus hypermobilizing the first ray. Supination (inversion) of the subtalar joint allows the first Metatarsal and Cuneiform 20 to rise above the Cuboid 21. In this or the neutral condition, the peroneus longus 19 passes obliquely through the transverse plane and is able to provide the required downward component of muscle force.
Such subtalar joint pronation may be directly caused by congenital rearfoot eversion or indirectly caused by compensation for a congenital forefoot varus. In either event, it is necessary to specifically address the rearfoot condition. Previously, this has been done by rearfoot posting, that is, the application of a wedge elevated on the medial aspect to force inversion of the rearfoot. Although the technique is effective, the angle of the wedge is critical and generally difficult to achieve accurately and comfortably. Moreover, a rearfoot wedge is a static, single action component usually fabricated from hard, non-shock absorbing materials.
Turning now to the physiological aspects of in-toe/out-toe, a frequently encountered problem, the conditions generally develop during childhood. The conditions are commonly referred to as in-toe (pigeon toed) or out-toe (crows feet). In-toe or out-toe gait results from a rotational force applied to the foot. This rotational force may be caused by anterior or posterior placement of the acetabulum (hip socket into which the femoral head fits) as well as by internal or external rotation of the femur (upper leg bone) or the Tibia (lower leg bone). Two conditions of the foot which may cause an in-toe gait are Talipes Equinovarus (clubfoot) or Metatarsas Adductus (congenital pigeon toed appearance). Some in-toe conditions may result as compensation for excess pronation but generally the reverse is true; excess pronation is compensatory for either in-toe or out-toe gaits.
In practice, the treatment for in-toe/out-toe gaits includes the use of a forefoot and rearfoot step. Using the in-toe gait as an example, a lateral step is placed on the forefoot and a medial step is placed on the rearfoot. When the forefoot encounters resistance on the lateral aspect during the propulsive phase of the gait cycle, the rearfoot is encouraged to adduct (rotate internally towards the mid-line of the body). Adduction of the rearfoot causes the forefoot to abduct, thus correcting for the in-toe gait.
The situation for the out-toe gait is exactly opposite; a step is placed on the medial aspect of the forefoot, causing the rearfoot to abduct (rotate externally away from the mid-line of the body). Consequently, the forefoot rotates internally, correcting for the out-toe gait.
In both in-toe and out-toe gait problems, previous treatment included the use of a medial rearfoot step to prevent eversion, thereby limiting pronation. However, a rearfoot step is only a static, single action component which does not embrace additional aspects of a pronating foot. Moreover, if the step is fabricated from soft materials, it breaks down rapidly and if the step is fabricated from hard materials, the angle is critical and it does not provide shock absorbing properties.